1. Field of the Invention
The invention relates to a vehicular rearview mirror assembly having multiple lens elements and mirror elements. In one aspect, the rearview mirror assembly has an image having minimal distortion and optimal accuracy.
2. Description of the Related Art
Mirrors are ubiquitous for contemporary vehicles. Vehicular mirrors have long been used to aid the driver in operating the vehicle, especially in improving the rearward view of the driver. Rearview mirrors are typically mounted to the exterior of the vehicle at the front of the driver's and front passenger's doors adjacent to the lower corner of the side windows. This places the rearview mirrors forward of the driver, where the driver can readily shift his line of sight from the road to the mirrors, and where the mirrors will not obstruct the driver's front and side vision. In order to provide a sufficiently large image for the driver's observation, the mirror assemblies are generally large and extend outwardly of the vehicle a significant distance.
Such external rearview mirrors can disrupt the aerodynamics of the vehicle and are susceptible to damage. Furthermore, the mirrors require frequent cleaning in order to maintain the quality of the image and any interruption in the light passing from the mirror through the window to the interior of the vehicle, such as a broken window or dirt, can render the mirror ineffective. Thus, attempts have been made to design a mirror assembly having a smaller size and providing a high-quality image regardless of the condition of the window.
U.S. Pat. No. 6,033,078 to Su et al., issued Mar. 7, 2000, discloses a multi-component rearview mirror unit comprising lenses and reflecting elements. However, the optical system disclosed in the Su et al. patent substitutes a focal system for an afocal system, produces an image that is fuzzy and distorted, produces an image that is insufficiently bright, produces an unacceptably high angular magnification, has a high weight and manufacturing costs, and can cause driver eye strain. Furthermore, the optical system disclosed in the Su et al. patent results in improper light path replication compared to a conventional mirror system. The input collimated light is converted to output diverging light, requiring eye refocusing. Additionally, the system lacks defining and limiting apertures. Artwork displays a lack of optical refraction at key surfaces which creates a light ray path error. The multiple curved lenses result in field distortion and small petzfal radii. Finally, the aspheric surfaces are inadequate for correcting image aberrations.